(a) Technical Field
The present invention relates to a method for controlling an on-board charger (OBC) of an eco-friendly vehicle, more particularly, to a method for controlling an OBC of an eco-friendly vehicle, in which the range of an AC input power frequency at which the charging operation of the OBC is possible can be widened without increasing the capacity of a power factor correction (PFC) capacitor.
(b) Description of the Related Art
In general, a plug-in hybrid vehicle, an electric vehicle, or the like, which are eco-friendly vehicles, include a high voltage battery, a traveling motor driven using the high voltage battery as a power source, an inverter for converting AC power into DC power in charging/discharging of the high voltage battery, and the like.
Particularly, a separate charger (also known as an on-board charger (OBC)) for generating charging current with respect to the high voltage battery by converting external power (e.g., power of electric vehicle supply equipment (EVSE) or household AC power) into rechargeable AC power is mounted in the eco-friendly vehicle. Accordingly, electric energy necessary for traveling is charged in the battery through the OBC from charging equipment, so that the driving of the eco-friendly vehicle is performed.
A battery charging method using the charger includes applying household AC power to the charger mounted in a vehicle; generating charging current by allowing AC power to be converted into DC power by the charger; and charging a high voltage battery by applying the charging current generated in the charger to the high voltage battery.
FIG. 1 (RELATED ART) is a configuration view illustrating an OBC of an eco-friendly vehicle.
As shown in FIG. 1, the OBC includes an AC power rectifier 10, a power factor correction (PFC) converter 12 for correcting a power factor, a DC-DC converter 14 for performing charging control by converting a voltage charged to a high voltage battery 16 into a DC voltage, and the like.
Particularly, the PFC converter 12 is configured between the AC power rectifier 10 and the DC-DC converter 14 in the OBC, in consideration that the improvement of the power factor is essentially required as the high voltage battery is charged using AC power.
An output capacitor 13 of the PFC converter 12 generates and outputs an output voltage ripple of a sine wave by absorbing input current (in the direction of the arrow in FIG. 1) following the rectification form of AC input power due to PFC control.
More specifically, the output capacitor 13 of the PFC converter 12 generates an output voltage ripple of a PFC capacitor (see FIG. 2 (RELATED ART), graph (a)) representing a sine wave by absorbing an input current ripple of the PFC capacitor (see FIG. 2 (RELATED ART), graph (b)) input to the output capacitor 13.
In this state, as shown in the following Equation 1 representing a correlation between the input current ripple of the PFC capacitor and the output voltage ripple of the PFC capacitor, the capacitor output voltage ripple of the PFC converter 12 is in proportion to the magnitude of an AC ripple flowing through the output capacitor 13, and is in inverse proportion to the capacity of the output capacitor 13 and an AC input power frequency.
                              Δ          ⁢                                          ⁢          V                =                  k          ⁢                                    Δ              ⁢                                                          ⁢              I                                      C              ·                              f                ac                                                                        Equation        ⁢                                  ⁢        1            
In Equation 1, ΔV represents an output voltage ripple of the PFC capacitor, ΔI represents an input current ripple of the PFC capacitor, C represents a capacity of the PFC capacitor, and fac represents an AC input power frequency.
According to Equation 1, the magnitude of the capacitor output voltage ripple ΔV of the PFC capacitor when the capacity of the PFC capacitor is identical to the input current ripple is changed depending on a frequency as shown in FIG. 3 illustrating the magnitude of an output voltage ripple of the PFC capacitor for each input power frequency.
More specifically, as the AC input power frequency decreases (low frequency), the magnitude of the output voltage ripple ΔV of the PFC capacitor increases. Particularly, if the AC input power frequency is decreased to a predetermined frequency or less, there occurs a case where the maximum value of the output voltage ripple ΔV of the PFC capacitor exceeds a PFC output over-voltage protection specification (protection range). Therefore, the operation of the PFC converter is temporarily impossible, and the charging operation of the OBC is also restricted.
In order to solve such a problem, a method was conventionally used which increases the capacity of the PFC capacitor in order to widen the range of an AC input power frequency at which the charging operation of the OBC is possible.
As shown in FIG. 4 (RELATED ART), as the AC input power frequency decreases, the required capacity of the PFC capacitor rapidly increases. Therefore, the capacity of the PFC capacitor should increase about two times greater than that of existing capacitors in order to extend 40 Hz that is an operating region of the existing capacitors up to 20 Hz.
However, as the capacity of the PFC capacitor is increased in order to widen the range of the AC input power frequency, an increase in cost of the OBC is caused, and the packaging performance in manufacturing of the OBC may be deteriorated.